It is well known that adsorbents, by their very nature, are susceptible to contamination from environmental sources. This contamination can result in the adsorbent exhibiting lowered adsorption capacity, reduced functionality, or reduced adsorption kinetics when used for its intended application. Typical unimpregnated adsorbents that are subject to lowered adsorption capacity and/or reduced adsorption kinetics due to environmental contamination include, but are not limited to, activated carbons, silica gels, molecular sieves, polymeric adsorbents, and zeolites. For the case of impregnated adsorbents, environmental contamination can also result in the loss of functionality for their designed purpose. This loss of functionality is a result of a physical or chemical interaction between the impregnant and the environmental contaminate which negatively impacts the desired functionality of the material.
Impregnated adsorbents include, but are not limited to metal, acid, base, salt, and/or organic compound impregnated activated carbons, silica gels, molecular sieves, polymeric adsorbents, and zeolites. Impregnated adsorbents are commonly used as catalysts. Impregnation of the adsorbent with said metal, acid, base, salt, and/or organic compound is typically accomplished by vapor phase deposition, solvent evaporation, solid--solid contact, and similar techniques well known to those skilled in the art.
Those skilled in the art involved in the manufacture, storage, and/or transport of unimpregnated and impregnated adsorbents are well aware of the numerous potential problems in handling adsorbents. As such, care is taken to minimize excessive exposure of the adsorbents to the local environment during processing and subsequent packaging. Packaging is typically selected so that exposure of the adsorbent to environmental contaminates during storage or transport is also minimized. Traditionally, drums, bags, and other types of containers have been used for packaging. These containers can be hermetically sealed to prevent subsequent contamination. However, the typical containers does not provide provision to identify instances where the sealing integrity has been lost, except in instances of obvious container failure. Also, the containers are typically sealed in an ambient air environment in which the entrapped air, at atmospheric pressure, may react with the adsorbent to degrade some of its properties. This degradation may be especially severe in the case of impregnated adsorbents.
The adsorbent, if powdered, granular, pelletized, spherical, or an other type of particulate, is generally "free-flowing" in such containers. As such, the individual particles of the adsorbent are free to move against each other. This movement normally occurs during vibration of the container as, for example, such during with transportation. The result of this movement is the attrition of the adsorbent particles which increases the amount of undesired undersize material in the container. Such attrition is most apparent with granular and pelletized adsorbents. Attrition can also result in an increase in packing density. Vibration during transport can also cause the packing density of the adsorbent to increase. Attrition and vibration can also lead to undesired particle segregation within a container.
In drums or other rigid containers, an increase in packing density results in headspace being created, which in the case of a fixed container produces voids. In non-rigid containers, such as bags, an analogous situation can develop. If the nonrigid container is hermetically sealed, the entrapped gases therein result in the formation of a void space as the packing density of the adsorbent increases. Any external force can pressurize the gases in the void volume, which can result in the hermetic seal being lost causing a complete container failure.
Environmental contamination of adsorbents during manufacture, storage, and/or transportation can also be reduced by packaging the contents under an inert atmosphere. While often effective such operations are difficult to carry out and generally expensive. A particularly significant problem associated with inert gas packaging is the removal of contaminate gases and vapors from the adsorbent prior to or during the inerting process. Likewise, packaging the material under vacuum using known techniques is can result in significantly higher packaging costs because of the specialized procedures used and the equipment required to perform such operations. Vacuum packaging of adsorbents is further complicated by the very nature of the adsorbents themselves. That is, adsorbents adsorb gases and vapors. Removal of such adsorbed gases and vapors from the adsorbent is know to be difficult and requires extensive "pumping-down" with an adequate vacuum source.
The ability of adsorbents to adsorb gases, even at low pressures is well known. Activated carbons have been used to store liquefied gases (U.S. Pat. No. 2,760,598) and as a means to maintain vacuum in closed vessels (U.S. Pat. No. 3,921,844). It is also know that cooling the carbon increases it's effectiveness. Adsorption differs from absorption in that it occurs when the concentration of gas molecules is greater on the surface of the solid that in the bulk phase, there is no chemical reaction involved and the process is reversible; whereas, absorption occurs only when there is bulk penetration of gas molecules into the structure of the solid.
Accordingly, it is the object of the present invention to provide a method for packaging adsorbents which provides improved packing densities, reduced attrition losses, and reduced exposure of the adsorbent to environmental or other contamination. It is further an object of the present invention to provide a method that assists in the identification of instances of packaging failure. It is also an object of the invention to provide a cost effective method for packaging adsorbents.